The strategy hinges on two molecular villains that have long frustrated oncologists. The first is enhancer of zeste homolog 2, or EZH2, the catalytic engine of the Polycomb repressive complex 2, which decorates histone proteins with repressive methylation marks and helps lock tumor-suppressor genes into silence. EZH2 is frequently overexpressed in colorectal cancer and has been linked to advanced disease, poor survival, and resistance to chemotherapy. The second is signal transducer and activator of transcription 3, or STAT3, a signaling hub whose hyperactivation drives proliferation, survival, invasion, and immune evasion. Crucially, these two are not independent actors: EZH2 activity has been shown to sustain STAT3 phosphorylation, creating a self-reinforcing loop that pushes cancer cells toward increasingly aggressive behavior.

Enter microRNA-124, a small regulatory RNA best known for its roles in the nervous system but increasingly recognized as a formidable tumor suppressor. The researchers began by mining publicly available clinical datasets, including the GEO repository entry GSE156719, and confirmed that miR-124 is significantly downregulated in colorectal cancer tissues. Strikingly, the loss of this microRNA correlated with more advanced tumor stages and poorer patient prognosis, echoing earlier independent reports that reduced miR-124 expression serves as an independent prognostic factor in colorectal cancer patients. Prior mechanistic work had established that miR-124 can directly target the EZH2 transcript, making it an attractive therapeutic cargo—if only it could be delivered effectively.

That delivery problem is precisely where the new study makes its mark. MicroRNAs are notoriously fragile molecules: injected freely into the bloodstream, they are rapidly degraded by circulating nucleases, fail to cross cell membranes, and get filtered out by the kidneys before reaching their targets. Synthetic nanoparticles can protect RNA cargo, but they often trigger immune reactions, accumulate in the liver and spleen, and lack any built-in ability to home in on tumors. The Tehran-led team instead turned to small extracellular vesicles, natural nanoscale membrane sacs ranging roughly from 30 to 150 nanometers, secreted by virtually all cells and acting as intercellular couriers for proteins, lipids, and genetic material.

Mesenchymal stem cells are particularly generous producers of these vesicles, and their cargo packets come with several built-in advantages. They are biocompatible, minimally immunogenic, stable in circulation, and—thanks to surface molecules inherited from their parent cells—they display a natural tropism for tumor tissue, navigating toward the inflammatory, hospitable terrain of the tumor microenvironment. To weaponize this delivery system, the researchers used lentiviral transduction to coax mesenchymal stem cells into overproducing miR-124, so that the microRNA became efficiently packaged into the vesicles the cells subsequently released. The result was a batch of engineered MSC-derived small extracellular vesicles, dubbed MSC-sEV-miR-124, brimming with the tumor-suppressive cargo.

Laboratory tests on colorectal cancer cells showed that the vesicles were readily internalized, delivering functional miR-124 into the recipient cells and restoring it to levels the cancer had suppressed. Once inside, miR-124 bound to its target sequence on EZH2 messenger RNA, directly downregulating the epigenetic silencer. The consequences cascaded through the cell: with EZH2 suppressed, STAT3 phosphorylation dropped, weakening the oncogenic signaling loop. Treated cancer cells lost their capacity for unrestrained proliferation, their migratory prowess diminished, and the epithelial-mesenchymal transition—the cellular makeover that lets tumor cells detach, invade surrounding tissue, and seed metastases—was visibly reversed. The team also observed that the treatment pushed cancer cells toward apoptosis, the controlled self-destruction program that malignant cells typically resist.

Perhaps the most clinically tantalizing finding emerged from combination experiments with 5-fluorouracil, a chemotherapy backbone drug for colorectal cancer. MSC-sEV-miR-124 sensitized the cancer cells to the drug and reversed chemoresistance, an effect the researchers attribute to the downregulation of EZH2, which earlier studies have implicated in therapy resistance through mechanisms including the suppression of autophagy. If this chemosensitizing effect holds up in further models, engineered vesicles could eventually be paired with existing drug regimens rather than replacing them, potentially lowering required doses and reducing the toxic side effects that plague current protocols.

The in vivo experiments provided the crucial proof of concept. When the engineered vesicles were administered in a xenograft model using BALB/c mice bearing colorectal tumors, tumor growth was significantly reduced compared with controls. Molecular analysis of the excised tumors confirmed that the intended mechanisms had engaged in living tissue: EZH2 and STAT3 signaling were downregulated, the proliferation marker Ki-67 diminished, and epithelial-mesenchymal transition markers receded. The vesicles had not only reached their targets but had executed the genetic program they were designed to deliver, suppressing the dual EZH2-STAT3 axis from within the tumor itself.

Significant hurdles remain before such a therapy could approach the clinic. Manufacturing extracellular vesicle therapeutics at pharmaceutical scale demands rigorous quality control over vesicle size, cargo loading efficiency, purity, and batch consistency—challenges that recent reviews of extracellular vesicle-based drug development have flagged as central to the field. Questions about long-term safety, dosing, biodistribution, and the behavior of mesenchymal stem cell-derived products in diverse patient populations will all need systematic answers. The authors themselves frame the work explicitly as proof of concept in murine models, noting that EV-based miRNA delivery warrants further investigation as a strategy to modulate the tumor microenvironment and overcome the epigenetic and oncogenic signaling barriers that currently limit colorectal cancer therapy.

Even so, the study adds an important datapoint to one of the most exciting convergences in modern oncology: the marriage of RNA therapeutics with biomimetic nanodelivery. By exploiting the tumor-homing talent of stem cell vesicles to smuggle a master-regulatory microRNA past the body’s defenses, and by aiming that microRNA at two intertwined pillars of cancer aggression simultaneously, the research outlines a template that could extend well beyond colorectal cancer. As the field of engineered extracellular vesicles matures, therapies that once lived only in molecular biology textbooks may be inching closer to the infusion clinic.

Subject of Research: Engineered mesenchymal stem cell-derived extracellular vesicles delivering miR-124 as a therapy for colorectal cancer

Article Title: Engineered mesenchymal stem cell-derived small extracellular vesicles delivering miR-124 suppress colorectal cancer progression through EZH2 downregulation and attenuation of STAT3 signaling

Article References: Behzadi Andouhjerdi, R., Hosseini, F., Hosseinzadeh, N., Zivari, S., Salkhordeh, S., Mohammadi, M., Rahmani, M., Hatami, P., Naji, S. S., Pourtahmasebi, M., Khanabadi, M., Golbahar, M., Hajesmaeili, A., Eftekhari, P., Asbaghi, M., Norouz-Nejad, A., Akbarabadi, P., Ghazimoradi, M. H., Babashah, S., & Piravar, Z. (2026). Engineered mesenchymal stem cell-derived small extracellular vesicles delivering miR-124 suppress colorectal cancer progression through EZH2 downregulation and attenuation of STAT3 signaling. Medical Oncology, 43(11), Article 318. https://doi.org/10.1007/s12032-026-03418-z

Image Credits: AI Generated

DOI: 10.1007/s12032-026-03418-z

Keywords: colorectal cancer, extracellular vesicles, mesenchymal stem cells, miR-124, EZH2, STAT3, epigenetics, microRNA delivery, 5-fluorouracil, chemoresistance, EMT, xenograft model